1. Field of the Invention
The present invention relates to a motion estimation system for compressing motion video data and, more particularly, to a half-pixel motion vector estimation apparatus capable of estimating a motion vector having half-pixel accuracy using peripheral blocks of video blocks corresponding to the motion vector which is estimated by pixel accuracy used in a differential pulse code modulation (DPCM) method of encoding a digital video signal. A motion estimation method having half-pixel accuracy is also disclosed.
Korean Patent Application No. 93-7917 is incorporated herein by reference for all purposes.
2. Discussion of Related Art
A variety of encoding methods have been proposed to effectively compress data for transmission by encoding a difference signal between the respective frames, primarily in video processing technology fields using a continuous digital video signal, e.g., high definition television, digital video cassette recorders and multi-media system, etc. DPCM encoding is a familiar example of such a method. Using the DPCM encoding process, data is compressed to a greater degree as the difference signal between frames grows smaller, i.e., when the video signal representing the difference between the respective frames of a television signal is encoded. For a still image having no movement between the frames, the difference signal between the frames becomes zero, thereby maximizing the data compression efficiency. However, the larger the movement between the frames, the larger the difference signal between the frames, thereby lowering the data compression efficiency.
In order to minimize this defect in the DPCM encoding method, one frame can be divided into a number of blocks, each of which has a predetermined magnitude. Then, the interframe motion is estimated for each block. Accordingly, the difference signal between the video blocks, which belong to a frame corresponding to and different from each other is transmitted by motion estimation, thereby enhancing the data compression efficiency.
The motion estimation is accomplished by comparing the video blocks within the previous frame with the video block within the present frame, both of which are created by the one pixel movement in the vertical and horizontal directions, and then finding the video block having the smallest difference signal. Since it is difficult in view of an actual system realization to compare each block of the present frame with the whole blocks within the previous frame, a search area having a predetermined magnitude corresponding to each block is set for the previous frames. The motion vector is then determined by search in that area. The smaller the size of the block, the more accurate the search for movement is, which increases the size of the motion vector. It should be noted that the larger the size of the search area becomes, the larger the movement which can be found in that search area, which increases the magnitude of the motion vector.
World Patent No. WO 93/16556 A1, which is commonly assigned to the assignee of the instant application, discloses a motion vector estimation method which has half-pixel accuracy and which uses a search area composed of the video block within the present frame having a pixel size of N.sub.1 and N.sub.2 and a video block within the previous block having a pixel size of M.sub.1 .times.M.sub.2. The above-identified world patent estimates motion vector having half-pixel accuracy using an error value based on the motion estimation. In contrast, British Patent Publication No. GB 2,236,449 A, published on Mar. 4, 1991, discloses a motion vector estimation method having half-pixel accuracy achieved through a sub-integer-pixel estimation method for the motion vector using a correlation function.